Quarterly report pursuant to Section 13 or 15(d)

Convertible Instruments and Accrued Interest - Preferred stock (Detail)

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Convertible Instruments and Accrued Interest - Preferred stock (Detail) - USD ($)
shares in Thousands, $ in Thousands
 9 Months Ended 12 Months Ended
Feb. 28, 2022
May 31, 2021
Class of Stock [Line Items]    
Accrued dividends $ 3,635 $ 2,647
Series B Convertible Preferred Stock    
Class of Stock [Line Items]    
Undeclared dividend $ 8 $ 18
Shares of common stock 17 36
Series C Convertible Preferred Stock    
Class of Stock [Line Items]    
Accrued dividends $ 1,886 $ 1,530
Shares of common stock 3,772 3,060
Series D Convertible Preferred Stock    
Class of Stock [Line Items]    
Accrued dividends $ 1,749 $ 1,117
Shares of common stock 3,498 2,234